Data from: Intra-ejaculate sperm selection in female zebra finches

Among internal fertilizers, typically fewer than 1% sperm survive the journey through the oviduct. Several studies suggest that the sperm reaching the ovum—the ‘fertilizing set’—comprise a non-random sub-population, but the characteristics of this group remain unclear. We tested whether oviductal selection in birds results in a morphologically distinct subset of sperm, by exploiting the fact that the fertilizing set are trapped by the perivitelline layer of the ovum. We show that these sperm have remarkably low morphological variation, as well as smaller head size and greater tail length, compared with those inseminated. Our study shows that the morphological composition of sperm—rather than length alone—influences success in reaching the ovum.在体内受精（internal fertilization）物种中，通常仅有不足1%的精子能够完成通过输卵管的旅程并存活。多项研究表明，抵达卵细胞的精子——即“受精群（fertilizing set）”——并非随机的亚种群，但该类精子的具体特征仍不明确。本研究借助受精群会被卵细胞的卵周层（perivitelline layer）捕获这一特性，探究鸟类的输卵管选择是否会产生形态学上独特的精子亚群。研究结果显示，与输精时的精子相比，这类受精精子的形态学变异程度极低，且头部尺寸更小、尾部长度更长。本研究证实，精子的形态学组成（而非单一的长度）会影响其抵达卵细胞的成功率。